.alpha.,.alpha.-Dichloroazoalkanes. I. Synthesis: Stereospecificity and side reactions. The crystal structure of 1,1'-dichloro-1,1'-diphenyl-1,1'-azopropane

Abstract

The 1,4 addition of chlorine to ketazines in methylene chloride at -60" is shown by nmr to proceed stereospecifically so that symmetric (syn,syn or anti,anti) ketazine isomers give meso-a,a '-dichloroazoalkanes and unsymmetric (syn,anri) ketazine isomers give the di product. Studies on equilibrium and nonequilibrium mixtures of ketazine isomers are reported. At low temperature addition is clean and does not involve radical chains, but at room temperature there is solvent dependent competition from ionic substitution of hindered ketazines and, in the light, from radical-induced decomposition of a-arylazoalkanes. Single crystal X-ray diffraction establishes the chlorine-nitrogen eclipsed conformation for meso-1,1 '-dichlofo-1,l '-diphenyl-1,l '-azopropane in the solid state with C-N and N=N bond distances of 1.46 and 1.24 j= 0.02 A, respectively. Thermolysis of this azo compound and of its dl diastereomer gives cage coupling with ~1 0 % stereospecificity.

1,2,4-Triazoles: Synthetic approaches and pharmacological importance. (Review)

“…These salts were directly subjected to hydrolysis with aqueous sodium bicarbonate to give, after loss of the CO 2 Et group, 1,2,4-triazole nucleosides of peracylated β-D-ribofuranoside 88a-c. Similarly, the β-D-galactopyranosyl-1,2,4-triazole nucleosides 89 were prepared [113] α,α'-Dichloroazoalkanes 92 were prepared by chlorination of ketazines 91 [121][122][123][124][125][126][127][128][129][130], which were obtained by reaction of 2 eq. of ketone 90 with 1 eq.…”

The electrochemical reduction of 1,4-dichloroazoethanes: Reductive elimination of chloride to form aryl azines

“…All 1-X/Y were synthesized in a fumehood by chlorination of the corresponding acetophenone azines (2-X/Y) and purified by recrystallization [19][20][21]. Excess chlorine gas was condensed into a round-bottom flask containing neat 2-X/Y or a suspension of 2-X/Y in CH 2 Cl 2 .…”

Structure and reactivity in highly halogenated ketazines

“…The chlorination of these azines has been studied in some detail (5). In the case of acetophenone azine either 1 ,4-addition to give the azo compound 8, or substitution, occurs cleanly, depending on solvent and temperature (Scheme 2).…”

“…In the case of acetophenone azine either 1 ,4-addition to give the azo compound 8, or substitution, occurs cleanly, depending on solvent and temperature (Scheme 2). One equivalent (5), or an excess, of C12 in methylene chloride at -70°C gives 8. In carbon tetrachloride only substitution is observed, 6 equivalents of C12 giving the hexachloro compound 9 at room temperature (5).…”

“…One equivalent (5), or an excess, of C12 in methylene chloride at -70°C gives 8. In carbon tetrachloride only substitution is observed, 6 equivalents of C12 giving the hexachloro compound 9 at room temperature (5). Lower levels of C12 gave the expected mixtures of partially chlorinated azines.…”